Combined operation for catalytically upgrading gasoline



Feb. l2, 1957 v. HAr-:NsEL Erm. 2,781,298

COMBINED OPERATION FOR cA'rALyTIeALLY UPGRADING GAsoLINE Filed March 14, 1952 @vwo nited tates Patent COMBINED OPERATION FOR CATALYTICALLY UPGRADING GASLINE Vladimir Haeusel, Hinsdale, and Clarence G. Gerhold,

Riverside, lll., assignors to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application March 14, 1952, Serial No. 276,654

7 Claims. (Cl. 19d-50) This invention relates to an improved operation for effecting the catalytic upgrading of gasoline, and more specifically to a combined process for selectively subjecting dierent fractions of a gasoline or naphtha charge stream to different octane increasing reactions in a manner obtaining improved yields of high grade product.

In substantially all of the various present catalytic reforming operations, a straight-run gasoline or naphtha stream is upgraded by effecting the contacting of suitable dehydrogenation and hydrocracking catalysts at conversion conditions providing aromatization and hydrocracking as a major reactions. To a lesser extent, there is some isomerization with live-membered ring naphthenes undergoing isomerization to six-membered ring naphthenes prior to conversion into aromatics. Also, there may be some degree of dehydrocyclization, wherein para ns are coverted directly into aromatics. However, even though the catalysts and the conversion conditions may be optimum for effecting selective hydrocracking, the hydrocracking operation provides a poor yield-octane relationship, since a portion of the charge stream does undergo cracking to form normally gaseous hydrocarbons that must be separated from the nal reformed stream. The dehydrogenation of naphthenes is also rather undesirable from the yield standpoint, since the aromatic product is denser than the parent naphthene, and particularly so with respect to the dehydrogenation of the C7 naphtheues. On the other hand, as will be discussed more fully hereinafter, it may be shown that the isomerization and dehydrocyclization of parain components may provide high octane numbers and high yields.

It is, therefore, a principal object of the present invention to effect the catalytic reforming and upgrading of gasoline and naphtha fractions in a manner which substantially precludes hydrocracking and resulting low yields of the high octane product stream.

It is a further object of the present invention to separate the gasoline charge stream into low and high boilingv fractions and to only isomerize the C7 and Ca fraction,

While effecting dehydrogenation, dehydrocyclization and isomerizaton of the heavier fraction whereby a resulting blended product stream provides a substantially higher octane yield relationship.

A still further object of the invention is to provide a modied operation where a dehydrogenated and dehydrocyclized heavier fraction is combined with a low boiling fraction prior to passing the latter into contact with an isomerizing catalyst at isomerizing conditions.

In a broad aspect, the present invention provides a method for selectively upgrading a gasoline or naphtha stream to ellect substantially improved yields of a high octane product, in a manner which comprises, separating the stream into low and high boiling fractions, passing the latter together with hydrogen into contact with a dehydrogenating and dehydrocyclizing catalyst at conversion conditions substantially precluding hydrocracking and effecting substantial aromatization of the naphthenic components and dehydrocyclization of paranic components thereof, passing the low boiling fraction into contact with a suitable isomerization catalyst at conversion conditions effecting the substantial isomerization of paranic hydrocarbons in the low boiling fraction, and recovering a resulting product stream to provide a high yield of gasoline having a high octane number.

In a preferable operation, hydrogen that is produced as a result of the dehydrogenation and dehydrocyclization of the high boiling fraction is separated and at least a portion is recycled in admixture with the high boiling fraction which is passed into contact with the dehydrogenation and dehydrocyclizing catalyst. Hydrogen is also made available, in a preferable operation, to pass with the low boiling fraction into contact with the isomerizing catalyst.

Further, in a particular desirable embodiment, the product stream resulting from contacting the high boiling fraction with the dehydrogenation and dehydrocyclizing catalyst passes through an isomerization zone in admixture with the low boiling fraction, which is subjected only to the isomerizing step. Thus, hydrogen formed during the dehydrogenating and dehydrocyclization steps directly with the heavier fraction and is present during the catalytic isomerization of the low boiling fraction and the hydrogen is present to benefit in the prevention ofcarbon formation on the catalyst and to aid in the isomerization reaction itself. This latter combined operation also requires but one separating zone for recovering a combined product stream and separating a gaseous hydrogen containing stream, and but one recycle line for returning at least in part of the hydrogen into admixture with the high boiling fraction.

Various dehydrogenating and dehydrocyclizing catalysts may be used to contact the high boiling fraction and effect the desired reactions with a minimum of hydrocracking, however, in accordance with the preferred operation of this invention a platinum-alumina-combined halogen catalyst, such as disclosed in Haensel Patent No. 2,479,110, issued August 16, 1949, provides a particularly desirable catalyst which provides high conversion yields with a minimum amount of carbon deposition so as to permit long periods of operation and catalyst contact without regeneration or replacement. Where more than one contacting zone is utilized in connection with the dehydrogenating and dehydrocyclizing step, it may be desirable to maintain a platinum-alumina-combined halogen catalyst within the dehydrocyclizing zone that contains somewhat more halogen content than that utilized within the dehydrogenating zone.

The isomerization catalyst which is utilzed to contact the low boling fraction of the charge, in accordance with the present invention, is also preferably a platinumalumina-combined halogen catalyst, although a lesser amount of platinum content may be incorporated in this catalyst, as compared with that utilized in the reactors for the dehydrogenating and dehydrocyclizing steps. Here again, particularly where the hydrocarbon stream undergoes conversion in the presence of hydrogen, the platinum-alumina-combined halogen catalyst permits long periods of operation with a minimum of carbon deposition.

It has been determined that the individual components of a gasoline or naphtha stream, containing C7 to C10 hydrocarbons, when processed differently may provide widely dilerent yield-octane relationships. For example, where a C7 fraction, having an F-l clear octane number of 54, is subjected to isomerization, so that the parans and naphthenes are isomerized to equilibrium, the octane number is increased to 72 with a yield of 100.2% by volume. Where a C7 fraction undergoes dehydrogenation, to the extent of about of the naphthenes pres` ent in the fraction, there results an octane number of 59.5

and a yield of- 95% by volume. Thus, it may be noted that it is particularly desirable, from the standpoint Yof superior yield octane relationship,` to eect the isomerization of the C1 hydrocarbons without dehydrogenation, as a preferred method of reaction as compared with the dehydrogenation of naphthenes: l

Where a C7 fraction undergoes both isomerization of paraihns and dehydrogenation of naphthenes, the overall yield is 93.8% by volume and an octane number of.77.5 is reached. Subsequent partial dehydrocyclizing of the same Cv fraction results ina yield of 90% by volume with an octane number of 84 clear. Thus, it may be noted that the dehydrocyclizing of the low boiling C7 fraction does not provide advantageous yields.

Where a C10 fraction, having an initialy octane number of 14? F-l clear, is subjected to isomerization' ot paraffins and naphthenes to an equilibrium condition, there results an octane number of 49 and a yield of 98.3% by volume. On the other hand, the dehydrogenation of naphthenes in the Cro fraction to the extentl of 95% conversion gives a product having an octane number of 34 and a yield of 95% by volume. The combined operation erlecting both isomerization of paraiins and dehydrogenation of naphthenes in the C10 fraction results in an octane number of 71 clear and a yield of 93.5% by volume. Subsequently, the dehydrocyclization of the Cio fraction produces an octane number of 90 clear and a yield of 90.05% by volume.

This data shows that the dehydrocyclization of the C10 fraction produces a higher yield octane relationship than the dehydrocyclization of the C7 fraction.

In accordance with the operation of the present invention, an improved overall yield octaneV relationship is obtained in a method which provides that the C1 and Cs fraction undergo isomerization under equilibrium conditions, and without eflecting dehydrocyclization, while the C9 and C10 fraction of a charge stream is permitted to undergo isomerization of the paratlins and naphthenes, substantial dehydrogenation of the naphthenes, and dehydroc rclization of the parans. An overall improved yield and octane number product stream may be obtained by blending the resulting streams from the separate conversions of the different fractions, or alternatively, in accordance with a particular embodiment of the present invention, the different fractions of the charge stream may be separated and treated so that the heavier fraction is subjected to dehydrogenation and dehydrocyclization prior to passing through an isomerizing zone together with the lower boiling C'i-Cs fraction, which undergoes isomerization only.

The advantages of the operation of the present invention which makes use of isomerizationin combination with dehydrogenation and dehydrocyclization, While substantially eliminating hydrocracking so as to obtain a better yield and octane number relationship, may be better set forth by reference to the following examples.

Example l 1000 volumes of a straight-run gasoline charging stock, having a clear F-l octane number of 31.5 and containing 454 volumes of a Cr-Cs fraction and 546 volumes of Cs-Clo fraction, is processed at a temperature of the order of about 900 F. and a pressure of about 500 p. s. i. g., under rconditions wherein hydrocracking is kept to a minimum while dehydrogenation of naphthenes, dehydrocyclization of parallins, and isomerization of parains is permitted to proceed to a maximum extent. The resulting product provides an octane number, F-1 clear, of 86.5 and a yield of 910 volumes of debutanized gasoline.

Example l1 1000 volumes of the same charging stock set forth in Example l, when subjected to somewhat less severe conditions, at a temperature of the order of about 880 F. and a pressure of the order of about 700 p. s. i. g., and

permitting hydrocracking', while eiecting dehydrogenation ot naphthelnes, dehydrocyclizaton of parains and isomerization of parains to a maximum extent, results ill a product stream having an F-l clear octane number of and a yield of 924 volumes of debutanized gasoline.

Example III 1000 volumes of a straight-run gasoline charging stock, such as set forth in Examples I and II, was fractionated to separate the material into 454 volumes of Cr-Cs fraction, and 546 volumes of Ce-Cio fraction. The C'z-Cs fraction, when subjected to catalytic reforming at a temperature of the order of about 850 F. and a pressure of about 500 p. s. i. g., so that the isomerization of parains and naphthenes is the primary reaction taking place, results in an increase in the octane number of the Cfr-Ca fraction from 45.0 to 65.8 with a yield of 451 volumes. When the Cta-C10 fraction is processed at a temperature of theorder of about 920 F. and a pressure ofabout 500 p. s. i. g., under conditions permitting dehydrogenation of naphthenes and both isomerization and dehydrocyclization of the paralhns, there is an increasev in the octane number from 65.8 to 106.2 and a yield of 480 volumes. Upon blending the two product streams, there is an overall yield of 931 volumes having an octane number of 86.7.

Example IV As in connection with Example III, 1000 volumes of straight-run gasoline stock was separated lnto 454 volumes of a Cfr-C8 fraction and 576 volumes of Cg-Cio fraction. When thek C'z-Ca fraction is subjected to isomerization, at a temperature of the order of about 830 F. and a pressure of the order of about 500 p. s. i. g., and with substantially n o dehydrogenation and dehydrocyclization, and the resulting product stream is blended with a resulting Cta-C10 fraction, which in turn is subjected to dehydrogenation of naphthenes and dehydrocyclization and isomerization of paraflins at somewhat milder conditions, with a temperature of the order of about 900 F. and a pressure of the order of about 500 p. s. i. g., then the blended product stream results in a yield of 945 volumes having an octane number of 80 F-l clear.

It may be further noted in comparing the above examples that there are particular advantages effected in separating the CP1-Ca fraction from the Cta-Cro fraction and processing each fraction at selected conditions and conversions which provide high octane numbers` and high volume recoveries. For example, in the operation of Example III where the charge stock is separated into the two separate fractions and each fraction is separately treated there is a resulting blended product stream giving an overall yield of 931 volumes having an octane number of 86.7 clear, while in Example I, the resulting product stream provided a yield of only 910 volumes within an octane number of 86.5 clear. Also, the final blended product stream resulting from the operation of Example IV gave an overall yield of 945 volumes having an octane number of 80 clear while the yield elected in the reforming of the charge stream under the conditions of Example Il resulted only in a yield of 924 volumes and an octane number of 80 clear.

Reference to the accompanying drawing and the following description thereof will aid in setting forth the irnproved combined operation of the present invention, while further advantages and features will be noted in connection therewith.

Referring now to the drawing, a straight-run gasoline or naphtha fraction is introduced by way of line 1 and valve 2 into a suitable Vfractionating column such as 3 in order that a low boiling fraction and a high boiling fraction may be obtainedto undergo separate conversion treatments in accordance with the present operation. The low boiling fraction, indicated as being Cs to Cs out is discharged from the upper portion of f ractionating column 3 by way of line 4 and valve 5, while the higher boiling fraction, indicated as a Cs-Cio cut, is withdrawn from a lower portion of the column by way of line 6 and valve 7. A small portion of bottoms, or material heavier than the Cio fraction, may be discharged from the lower end of the fractionator 3 by way of line S and valve 9.

The higher boiling Cs-Cio fraction is admixed with a hydrogen stream obtained from line 10 and the mixture passed through a heating zone 11 into line 12 and a rst reaction zone 13. In accordance with the present invention, the catalytic conversion eliected on the higher boiling fraction is carried out in a manner substantially precluding hydrocracking, and to thereby minimize losses in product yield. Thus, the hydrocarbon stream introduced into reactor 13 is maintained at a temperature of the order of about 920 F. and a pressure of the order of about 525 p. s. i. g. As set forth hereinbefore, the catalyst in reactor 13 is preferably a platinum-alumina-combined halogen catalyst suitable to effect dehydrogenation of the naphthenic components of the Cta-C10 fraction. The principal reaction in reactor 13 will comprise aromatization to form aromatic hydrocarbons and to a lesser extent dehydrocyclization and isomerization of parainic components in this fraction. The product stream from reactor 13 is passed by Way of line 14, intermediate heater 15, and line 16, into a second stage of primarily dehydrogenation Contact, that is provided by reactor 17. The product stream from the rst stage reactor 13 is reheated to a temperature of about 920 F., which is substantially the same as that provided for the introduction of the stream into reactor 13. However, there may be a somewhat lower pressure within reactor 17 than in reactor 13, by reason of the resulting pressure drop sustained through the iirst reactorand the heater 15, so that the pressure within reactor 17 is of the order of about 500 p. s. i. g. A platinum-alumina-combined halogen catalyst is also maintained in reactor 17 in order that there may be further dehydrogenation of the heavier fraction to form aromatic hydrocarbons, together with a minor amount of dehydrocyclization and isomerization. Since the dehydrogenation reaction is more rapid than dehydrocyclization and isomerization reactions, it is the principal reaction in reactors 13 and 17. In particular, the five-membered ring and six-membered ring naphthenic components are dehydrogenated in the reactor 17. The product stream from reactor 17 passes by way of line 18, valve 19, heater 20 and line 21 into a third catalyst containing reaction zone 22. In this latter reactor, the hydrocarbon stream undergoes primarily dehydrocyclization of the parainic components of the stream. The dehydrocyclization catalyst, as hereinbefore set forth, may also comprise a platinumalumina-combined halogen catalyst, however, the catalyst may contain a larger amount of halogen than is utilized in the catalyst for the dehydrogenation reactors 13 and 17. Heater reheats the product stream from reactor 17 to provide an inlet temperature of the order of about 920 F., while the contacting pressure will again be reduced by reason of pressure drop in the system, so as to provide a pressure in reactor 22 of the order of about 475 p. s. i. g.

The resulting dehydrogenated and dehydrocyclized C9C1o fraction passes from the reactor 22 by way of line 23, and valve 24 to an isomerization reactor 25, where it undergoes contact with an isomerization catalyst while in admixture with the low boiling fraction obtained from fractionator 3. The hydrogen to hydrocarbon ratio utilized for the high boiling fraction through the series of reactors 13, 17 and 22 is preferably high, say of the order of about 8 to l or 10 to 1 and may be still higher as hydrogen is produced from the dehydrogenation and dehydrocyclization reactions. The liquid hourly space velocity of the Cea-C10 fraction passing through the same reactors may vary in the range of from about 0.5 to about 20, however, preferably is at least about 3.

It is to be noted that the product stream from reactor 22 is not subjected to additional heating, but may be cooled or may pass, at the resulting temperature following the dehydrocyclization contact, directly into the isomerization reactor 25. The low boiling Cs-Cs fraction, passing by way of line 4 from fractionator 3, is subjected to heating in a suitable zone 26 to provide a temperature of the order of about 850 F. and then passes by way of line 27 into line 23, to become admixed with the dehydrogenated and dehydrocyclized higher boiling fraction in the latter line.

In the isomerization reactor 25, the mixed high and low boiling fractions and particularly the unconverted low boiling fraction undergo isomerization of the paraiinic components at a temperature of the order of about 850 F. while at a pressure of the order of about 450 p. s. i. g. It is not believed that pressure is particularly critical within the isomerization reactor and thus may vary somewhat from the 450 p. s. i. g. which has been designated, however, in a commercial unit, it is desirable to obviate a pump or compressor in the line between the dehydrocyclization and isomerization reactors so that as a result the pressure within the reactor 25 may be that which results from the passage of the hydrocarbon stream from reactor 22.

The catalyst maintained with reactor 25 also preferably comprises a platinium-alumina-combined -halogen catalyst,

which provides a very desirable isomerization catalyst having a long life and subject to but little carbon formation while being contacted with the hydrocarbon stream in the presence of hydrogen. The hydrogen to hydrocarbon ratio may be somewhat lower than that maintained in the dehydrogenation and dehydrocyclization reactors, Isay of the order of about 4 to l. A lower ratio of course results from the introduction of the low boiling fraction into admixture with the product stream from reactor 22. The liquid hour space velocity within the isomerization reactor 25 may also vary to some extent but is preferably in the range of from about l to 5.

It may be further pointed out that the catalyst distibution among the reactors is somewhat critical in View of the type and rate of the conversion reactions taking place in the present upgrading operation. The isomerization reaction while relatively rapid, tends to be a somewhat slower reaction than that of dehydrogenation and it is, therefore, desirable to maintain approximately 50% of the catalyst inventory within reactor 2S. While on the other hand, the rst stage dehydrogenation reactor 13 may utilize a catalyst content of only about 10% of the inventory, the second stage dehydrogenation reactor 17 about 20% of the catalyst inventory, and dehydrocyclization reactor 22 about 20% of the catalystinventory.

The resulting'combined product streams which leave the isomerization reactor 25 pass by way of line 28, valve 29, cooler 30 and line 31 into a suitable separating chamber 32. In separator 32, a hydrogen containing gaseous stream is discharged overhead, by way of line 33, and a high octane gasoline product stream is discharged by way of line 34 and valve 35. A portion of the gaseous hydro gen containing stream may be vented by way of line 36 and valve 37, while the remaining portion passes by way of valve 38 to compressor 39, and from the latter by way of line 10 into line 7 where it is recycled into admixture with the high boiling C9-C1o fraction, as hereinbefore set forth. The liquid gasoline stream discharged by way of line 34 from separator 32, is indi-cated as being passed into a stabilizer column 40. C3 and lighter components are discharged overhead from column 40 by way of line 41 and valve 42, while C4 and heavier components providing a high octane gasoline are withdrawn from the lower end of the column 40 by way of line 43 and valve 44.

It is to be noted that the foregoing drawing is strictly diagrammatic and additional equipment such as pumps, valves and the like may be needed to provide a desirable operating unit. For example, pumps would be needed in connection with lines 4 and 6 to provide for the charge of the liquid hydrocarbon fractions through the subsequent portions of the unit.

In an alternative method of operation within the scope of the present invention, the low boiling Cs-Cs fraction mayV pass through an isomerization zone to effect contact with the catalyst without being in admixture with the resulting product stream from the high boiling fraction. In other words, the dehydrogenated and dehydrocyclized fraction may pass from reactor 22 through line 23 and a line 45, having valve 46, to line 2S and then combined with the isomerized low boiling fraction iust prior to being cooled and passed to the separator 32. In still another instance, separate cooling and separating zones may be provided for each of the fractions and resulting combined product streams subsequently passed to a stabilizer column. Itis, however, desirable to have hydro gen present for the isomerization reaction so that a portion of the recovered hydrogen is in this alternative operation passed into adrnixture with the Cs-Cs fraction by way of line and a connecting line 47, having valve 48, prior to its passage into heater 26 and into contact with the isomerization catalyst within reactor 25. The hydrogen, as hereinbefore noted, is advantageous in -aiding the desired isomerization reaction and in preventing carbon formation on the catalyst.

We claim as our invention:

l. A method for selectively upgrading a gasoline stream to effect a substantially improved yield of high octane product, which comprises, separating said stream into a fraction containing Cs vand lower boiling hydrocarbons and 'a higher boiling fraction containing predominantly C9 and Cio hydrocarbons, pas-sing the latter fraction together with hydrogen into contact with a dehydrogenating and d ehydrocyclizing catalyst at conversion conditions substantially precluding hydrocracking and effecting substantial laromatization of naphthenic components and dehydrocyclization of paraliuic components thereof, passing a resulting dehydrogenated and dehydrocyclized stream into admixture with said lower boiling gasoline fraction 'and subsequently contacting the mixture with a `suitable isomerization catalyst at conversion conditions eiecting the substantial isomerization of the parain-i-c hydrocarbons'therein, cooling and separating the resulting combinedproduct stream passing from said isomerization contact to provide a gaseous hydrogen containing stream and a high yield of a liquid hydrocarbon stream having a high octane number, and returning at least a portion of the hydrogen containing gaseous stream into admixture with said high boiling fraction `as the aforesaid hydrogen stream passing therewith.

2. A method for selectively upgrading a gasoline stream to effect a substantially improved yield of high octane product, which comprises, separating said stream into a fraction containing Ca and lower boiling hydrocarbons and a higher boiling fraction containing predominantly C9 and C10 hydrocarbons, passing the latter fraction together with hydrogen into contact with a platinum-alumina-combined halogen dehydrogenating catalyst at conversion conditions effecting the substantial aromatization of naphthenic components therein and substantially precluding hydrocracking, subsequently passing this aromatized fraction together with hydrogen into contact with a platinum-alumina-combined halogen catalyst at dehydrocyclizing conversion conditions suitable to substantially dehydrocyclize paraflinic components in said fraction, passing the resulting dehydrogenated and dehydrocyclized stream into admixture with said low boiling fraction containing Ca and lower boiling hydrocarbons and introducing the mixture into contact with a platinum-alumina-combined halogen isomerization catalyst at conversion conditions effecting the substantial isomerization of the parainic hydrocarbons within said low boiling fraction, cooling and separating the resulting combined product stream withdrawn from said isomerization contact and providing a gaseous hydrogen containing stream and a high yield of a liquid hydrocarbon stream having a high octane number, and returning at least a portion of the hydrogen containing gaseous stream into admixture with said Cs-Cm fraction passing into contact with said dehydrogenation catalyst.

3. The method of claim 2 further characterized in that said Cs-Cio fraction undergoes aromatization in contact with said dehydrogenation catalyst at a temperature of the order of about 920 F. and a pressure of the order of about 525 p. s. i. g., said aromatized fraction is reheated to a temperature of the order of about 920 F. and undergoes dehydrocyclization in contact with said dehydrocyclizing catalyst at a pressure of the order of about 475 p. s. i. g., said low boiling fraction is heated to a temperature of the order of about 850 F. and the dehydrogenated and dehydrocyclized high boiling fraction is passed without added heat into admixture with said low boiling` fraction, and the resulting mixture contacts said isomerization catalyst at a temperature of the order of about 850 F. and a pressure of the order of about 450 p. s. i. g.

4. r1`he method of claim 3 still further characterized in that a greater quantity of catalyst is utilized in effecting said isomerization contact than contacts said C9-C1n fraction for electing said aromatization and greater than that contacting aromatized stream in effecting said dehydrocyclization and said isomerization catalyst contains less platinum content than that utilized within said dehydrogenating and dehydrocyclizing contacting steps.

5. A gasoline reforming process which comprises separating from the gasoline a light fraction containing C1 and Ca hydrocarbons and a heavier fraction containing C9 and C10 hydrocarbons, subjecting said heavier fraction to catalytic dehydrogenation and dehydrocyclization at conversion conditions substantially precluding hydrocraexing, commingling the thus treated heavier fraction with saidlight fraction, and contacting the resultant mixture with an isomerization catalyst at conversion conditions effecting isomerization as the principal reaction in this contacting step.

6', The process of claim 5 further characterized in that said heavier fraction is subjected first to dehydrogenation and then to dehydrocyclization in successive catalytic conversion stages.

7, The process of claim 6 further characterized in that each of the conversion reactions is effected in the presence of a catalyst comprising platinum and alumina and in that the isomerization stage contains approximately of the total catalyst employed in the process.

References Cited in the le of this patent UNTTED STATES PATENTS 

1. A METHOD FOR SELECTIVELY UPGRADING A GASOLINE STREAM TO EFFECT A SUBSTANTIALLY IMPROVED YIELD OF HIGH OCTANE PRODUCT, WHICH COMPRISES, SEPARATING SAID STREAM INTO A FRACTION CONTAINING C3 AND LOWER BOILING HYDROCARBONS AND A HIGHER BOILING FRACTION CONTAINING PREDOMINANTLY C3 AND C10 HYDROCARBONS, PASSING THE LATTER FRACTION TOGETHER WITH HYDROGEN INTO CONTACT WITH A DEHYDROGENATING AND DEHYDROCYCLIZING CATALYST AT CONVERSION CONDITIONS SUBSTANTIALLY PRECLUDING HYDROCRACKING AND EFFECCTING SUBSTANTIAL AROMATIZATION OF NAPHTHENIC COMPONENTS AND DEHYDROCYCLIZATION OF PARAFFINIC COMPONENTS THEREOF, PASSING A RESULTING DEHYDROGENATED AND DEHYDROCYCLIZED STREAM INTO ADMIXTURE WITH SAID LOWER BOILING GASOLINE FRACTION AND SUBSEQUENTLY CONTACTING THE MIXTURE WITH A 